Prolonged reduction or loss of blood pressure in a patient severely limits the amount of tissue perfusion of the patient and therefore causes damage to or death of the tissue. Although some tissues can tolerate hypoperfusion for long periods of time, the brain, heart and kidneys are very sensitive to a reduction in blood flow. Thus, during and after medical procedures and at other times, blood pressure is a frequently monitored vital sign. Blood pressure can be affected by the type of medical procedure performed and by physiological factors such as the body's reaction to the medical procedure. Moreover, blood pressure is often manipulated and controlled using various medications. Medical procedures, physiological factors, and medications can cause the blood pressure of a patient to change rapidly.
The traditional method of measuring blood pressure is with a stethoscope, occlusive cuff, and pressure manometer. However, this technique is slow, subjective in nature, involves the intervention of a skilled clinician, and often does not provide timely measurements. Blood pressure cuff instruments make only spot-check measurements, so repetitive interval measurements are often used to trend patient status. More frequent intervals improve vigilance at the expense of patient discomfort and possible patient injury (e.g., due to occlusion of blood vessels or nerve damage).